Thai National Parks

Species of Thailand

Yellow-bellied sea snake

Hydrophis platurus, Carolus Linnaeus, 1766

(In Thai: งูชายธงหลังดำ, ngu chay thong lang damm)

Pelamis platura, commonly known as the yellow-bellied sea snake, yellowbelly sea snake, or pelagic sea snake, is a species of sea snake found in tropical oceanic waters around the world, excluding the Atlantic Ocean.

It is the only member of the genus Pelamis.


The body of this snake is compressed, with the posterior less than half the diameter of the neck; the body scales are juxtaposed, subquadrangular in shape, and in 23–47 rows around the thickest part of the body; ventral scales, 264–406 in number, are very small and, if distinct, divided by a longitudinal groove, but usually are indistinguishable from adjacent body scales. The head is narrow, with an elongated snout; head shields are entire, nostrils are superior, and nasal shields are in contact with one another; the prefrontal scale is in contact with second upper labial; one or two preoculars, two or three postoculars, and two or three small anterior temporals are present; seven or eight upper labials are found, with four or five below the eye, but separated from the border by a subocular. Colors of the snake are variable, but most often distinctly bicolored, black above, yellow or brown below, with the dorsal and ventral colors sharply demarcated from one another; ventrally, there may be a series of black spots or bars on the yellow or brown background, or the yellow may extend dorsally so there is only a narrow middorsal black stripe, or a series of black crossbars. Total length for males is up to 720 mm, for females up to 880 mm; tail length for males is up to 80 mm, females up to 90 mm.


These snakes breed in warm waters; they are ovoviviparous with a gestation period around 6 months. According to Ditmars, females bear live young in tidal pools. They are helpless on land, and they sometimes form large aggregations of thousands in surface waters. These snakes use their neurotoxic venom against their fish prey. No human fatalities from envenomation are known.

As they live only in the ocean, they must get all of their food and water there. However, they do not have the ability to filter all the salt from seawater, although they can do it for food. To survive severe dehydration, they wait for months until the rainy season, when rainwater sits on top of the heavier saltwater below, then drink the surface water with lower salt concentration.


The yellowbelly is the most widely distributed sea snake and is capable of living and giving birth entirely in the open sea (it is completely pelagic), being found in all coastal waters around the rim of the Pacific Ocean except Alaska south to southern California, and in the coastal waters of the Indian Ocean from the Persian Gulf eastwards. It is the only sea snake to have reached the Hawaiian Islands. The sea snake has also been reported around the shores of New Zealand, a country that would otherwise be free of snakes were it not for the infrequent visits of yellowbellies and banded sea kraits.

The yellowbellied sea snake (Pelamis platura, previously known as Pelamis platurus) has also been reported to occur in the Agulhas Current along the east coast of Southern Africa. A specimen was found washed ashore (01-09-2014) after a storm and deposited on the sandy beach at Boesmansrivermouth, (near Port Alfred), Easter Cape Province, South Africa.

Yellowbellies (and all other sea snakes) are not found in the Atlantic or Mediterranean, though the water there is warm enough. Yellowbellies require a minimum of 16–18°C (60.8 to 64.4°F) to survive long term. Yellowbellies have not migrated around the southern tips of South America or South Africa because water temperatures are too cool. In October 2015, yellowbellies were reported and photographed on beaches in Ventura County, California, well outside their normal range, for the first time in 30 years. This change is believed to be associated with higher than usual coastal water temperatures associated with el Niño.

A land bridge formed (at Panama) between North and South America about 3 million years ago, making it impossible for them to enter the Caribbean Sea from the Pacific. If they had reached the eastern Pacific Ocean before the land bridge formed, they would almost certainly be found now in the Atlantic. The Panama Canal has not made a crossing of the isthmus possible because it is fresh water.

They do not live in the Red Sea because of its excessive salinity.


The yellowbelly seems to have evolved from the terrestrial elapids of Asia and Australia about 10 million years ago. This air-breathing sea snake has developed a flat, oar-like tail and valved nostrils since leaving the land millions of years ago.


Sea snakes are closely related to the venomous Australian snakes of the family Elapidae, but are sometimes classified in a separate family, the Hydrophiidae. Two subfamilies have been listed in the past, the sea kraits (Laticaudinae), and the true sea snakes (Hydrophiinae), though recent work suggests this subfamilial division may be inappropriate.

In 1766, Linnaeus published the original description of the yellow-bellied sea snake, naming it Anguis platura (Anguis meaning snake). In 1803, Daudin created the new genus Pelamis and assigned this species to it, referring to it as Pelamis platuros. In 1842, Gray described what he thought was a new species and called it Pelamis ornata (subsequently P. ornata became a synonym of P. platura). The word Pelamis is a feminine noun and means young or small tunny fish. In 1872, Stoliczka introduced the name Pelamis platurus (still the most used scientific name by scientists today), but used the incorrect ending -us instead of -a which a feminine noun requires. A few recent examples exist of scientists' beginning to use the grammatically correct name Pelamis platura, e.g., Bohme 2003 and the Reptile Database with its page headed Pelamis platura (Linnaeus, 1766), which includes an extensive synonymy of the different scientific names which have been used for the yellowbelly sea snake.


The genus name Pelamis is derived from the Ancient Greek word for "tunny fish", which presumably refers to the habitat or what Daudin thought they ate. The specific name platurus is a combination of the Ancient Greek words platys "flat" and oura "tail", referring to the flattened tail.


The venom of this species is highly potent, like other sea snakes. The subcutaneous of the venom is 0.067 mg/kg and the venom yield per bite is 1.0–4.0 mg.


Sea snake venom can cause damage to skeletal muscle with consequent myoglobinuria, neuromuscular paralysis or direct renal damage. The venoms of significant species of sea snake are neutralised with Commonwealth Serum Laboratories Ltd (of Melbourne, Australia) sea snake (Enhydrina schistosa) antivenom. If that preparation is not available, tiger snake or polyvalent antivenom should be used. No deaths have been recorded from bites in Australian waters. The E. schistosa antivenom was tested specifically on Pelamus platurus, and it effectively neutralised the venom.

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Scientific classification

Hydrophis platurus

Common names

  • German: Plättchen Seeschlange
  • English:
    • Yellowbelly sea snake
    • Pelagic sea snake
  • Thai: งูชายธงหลังดำ, ngu chay thong lang damm


  • Pelamis platurus, Tanya Chan-Ard et al. (2015)
  • Pelamis platurus, Harold Cogger (2014)
  • Pelamis platura, Van Stanley Bartholomew Wallach et al. (2014)
  • Pelamis platura, Brian I. Crother et al. (2012)
  • Hydrophis platurus, Kate Laura Sanders et al. (2012)
  • Pelamis platurus, S. Wilson & G. Swan (2010)
  • Pelamis platurus, Nguyen Van Sang et al. (2009)
  • Pelamis platyura [sic], Indraneil Das & Norsham S. Yaakob (2007)
  • Pelamis platurus, R.C. Sharma (2004)
  • Pelamis platurus, Alan E. Leviton et al. (2003)

Conservation status

Least Concern (IUCN3.1)

Least Concern (IUCN3.1)


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Pelamis platura
Pelamis platura

Range Map

Distribution map of Yellow-bellied sea snake, Hydrophis platurus in Thailand
  • Chanthaburi Coast
  • Chumphon Coast
  • Phuket Coast
  • Rayong Coast
  • Sirinat National Park
Range map of Hydrophis platurus in Thailand